Recently, we have identified stem cells (ISCs) in the Drosophila adult midgut that replenish the intestine throughout the entire lifetime of the animal. Drosophila ISCs, like vertebrate ISCs, are multipotent, producing both enterocytes and enteroendocrine cells. Furthermore, as in vertebrates, Drosophila ISCs utilize Notch signaling to produce an appropriate fraction of enteroendocrine cells and enterocytes. The relatively small cell number and simplicity of the Drosophila midgut allows one to identify ISCs morphologically under various conditions. Moreover, it is possible to remove gene function in marked clones of these cells in order to decipher the nature and directionality of signaling events. Based on our findings we will take advantage of the anatomically simpler but functionally relevant Drosophila system to address the following three specific aims. 1. Determine the cellular and molecular mechanisms that maintain Drosophila ISCs in a stem cell niche. 2. Identify the effects of nutrients, insulin signaling, and developmental signaling pathways like wingless and hedgehog on stem cell division, stability and differentiation. 3. Study how intercellular signals and environmental factors control the differentiation of enteroendocrine cells. HEALTH RELEVANCE. We have previously shown the maintenance and function of the adult Drosophila midgut bears many striking similarities to that seen in the human intestine. Therefore the results of our research should provide valuable insights into the pathogenesis of human digestive disorders such as intestinal cancers, malabsorption syndromes, and diabetes.